Influence of X-ray dose fractionation on the frequency of somatic mutations induced in Tradescantia stamen hairs

X-rays were used to investigate the influence of dose fractionation on the induction of pink and colorless somatic mutations in stamen hair cells of Tradescantia clone 02. Inflorescences were exposed to a single acute dose of 60 rad, two acute doses of 30 rad, or three acute doses of 20 rad. The dose rate in all cases was 30 rad/min. Intervals between dose fractions were varied from 35 sec to 48 h and the mutation frequency was compared with that resulting after the single dose of 60 rad. The date show a reduction in mutation frequency for fractionation intervals longer than 15 and 6 min for pink and colorless mutations, respectively, but not for shorter intervals. One interpretation of the data predicts that pink mutation frequencies are reduced by 11% for fraction intervals of 30 min to 6 h, and that colorless mutation frequencies are reduced by 24% for intervals of 15 min to 6 h. The corresponding sparing effect of dose fractionation is equal to 6 rad for pink mutations and 9 rad at the colorless mutation endpoint. A calculation has been made which indicates that the percentages of the total repairable (presumably two-hit) damage that is repaired during fraction intervals up to 6 h, are 16 and 35% for pink and colorless mutations, respectively